Claims that a "senior aide of a former prime minister" had links to a member of a paedophile ring are being examined by police.

Labour MP Tom Watson alleged during Prime Minister's Questions last week that a file of evidence used to convict Peter Righton of importing child pornography in 1992 contained "clear intelligence" of a sex abuse gang.

He claimed that a member of the group had bragged about links with a senior aide to a former prime minister. Mr Watson has written to Scotland Yard about the case.

Metropolitan Police commissioner Bernard Hogan-Howe said: "We've started to look into those claims, we haven't got too much detail yet.

"Tom Watson's indicated a particular concern around some individuals, we'll talk to him and we'll look to see what strength there is in those allegations.

"It's been handed over to a senior officer to look at, to talk to Tom Watson at the right stage to see what his source of information is. We will treat it seriously.

"Formally we'd need a complainant and at this stage I don't think we have a complainant, we've got someone who is pointing us towards a complainant."

He said that officers will aim to speak to Mr Watson this week, and to find out if there is "corroborating fact".

The MP said: "I'm grateful that the Metropolitan Police is taking this seriously. My greatest concern is that the documents seized upon the arrest of Peter Righton in the early 1990s are kept secure at the Met and fully reviewed.

"If this is done I'm sure it will yield clear intelligence of greater wrongdoing."